1. Field of the Invention
The present invention relates to a photo acid generator, a chemically amplified resist composition containing the photo acid generator, and a patterning process using the chemically amplified resist composition.
2. Description of the Related Art
In recent years, as LSI advances toward a higher integration and a more rapid processing speed, finer pattern rules are being requested. In this trend, a far ultraviolet lithography and a vacuum ultraviolet lithography are promising for the next generation fine patterning technologies. Especially, a photolithography using an ArF excimer laser light as a light source is an indispensable technology for an ultrafine patterning process with a size of 0.13 μm or less.
The ArF lithography started to be used partially from the fabrication of 130-nm node devices, and then it became a main lithography technology from 90-nm node devices. As the lithography technology for the next 45-nm node devices, a 157-nm lithography using a F2 laser was initially considered as a promising technology; however, a delay in development thereof due to several problems was indicated. Accordingly, an ArF immersion lithography rapidly emerged. In the ArF immersion lithography, a liquid whose refractive index is higher than air, such as water, ethylene glycol, and glycerin, is placed between a projection lens and a wafer. This enables the number of aperture (NA) of the projection lens to be designed so as to be 1.0 or more, thereby attaining a high resolution (for example, see Non-Patent Document 1); and this is now in the stage of practical use. For this immersion lithography, a resist composition not readily eluting into water is being requested.
In the ArF lithography, in order to prevent deterioration of a precise and expensive optical material, a highly sensitive resist composition that can express a sufficient resolution with a small exposure dose is requested. To realize this, the most generally used method is to select each component having a high transparency at a wavelength of 193 nm. For example, as to a base resin, polyacrylic acid, derivatives thereof, norbornene-maleic anhydride alternating copolymer, polynorbornene, ring-opened metathesis polymers, hydrogenated ring-opened metathesis polymers, and the like have been proposed; and these bring a certain level of results in enhancing a transparency of a resin.
Also, in recent years, a negative tone resist by an organic solvent development as well as a positive tone resist by an alkaline development has been receiving an attention. In order to resolve a very fine hole pattern, which cannot be achieved by a positive tone exposure, by a negative tone exposure, a negative pattern is formed by an organic solvent development using a positive resist composition having a high resolution. In addition, an attempt to double the resolution by combining two developments of the alkaline development and the organic solvent development is under study.
As to the ArF resist composition for the negative tone development by an organic solvent, an existing positive ArF resist composition can be used; and patterning processes using these are disclosed in Patent Document 1 to 3.
Also, an electron beam lithography has been utilized as ultrafine patterning technology as well as the ArF lithography, and has become indispensable as a method for processing a photomask blank in producing a photomask used for semiconductor manufacturing.
Generally, as a base polymer of a positive resist composition for an electron beam or an extreme ultraviolet (EUV), a material whose acid-labile protective group that protects an acidic functional group of a phenolic side chain contained in the base polymer is deprotected by an acid catalyst generated from a photo acid generator by high energy beam exposure thereby being made soluble in an alkaline developer is mainly used. As the acid-labile protective group mentioned above, a tertiary alkyl group, a tert-butoxycarbonyl group, an acetal group, and the like have been mainly used. Here, the use of a protective group having a relatively low activation energy required for deprotection, such as an acetal group, can advantageously provide a resist film with high sensitivity. However, if diffusion of the generated acids is insufficiently controlled, deprotection reaction takes place even in an unexposed part of the resist film, thereby causing problems such as deterioration of line edge roughness (LER) and decrease in in-plane uniformity of the pattern line width (that is, CDU: Critical Dimension Uniformity).
Thus, in accordance with a rapidly request for miniaturization, the effect of acid diffusion on lithography performance becomes further serious in a resist composition. This is because the pattern size is approaching the acid diffusion length, whereby resolution, LER, etc. are deteriorated. Accordingly, to gain more benefits from a shorter wavelength of a light source and a higher NA, suppression of acid diffusion is necessary ever than before in the material.
One of effective means for controlling acid diffusion is to introduce a bulky substituent or a polar group into a photo acid generator. Patent Document 4 discloses a photo acid generator having 2-acyloxy-1,1,3,3,3-pentafluoropropane-1-sulfonic acid that is excellent in solubility into a resist solvent and stability and allows various molecular designs. In particular, a photo acid generator having 2-(1-adamantyloxy)-1,1,3,3,3-pentafluoropropane-1-sulfonic acid into which a bulky substituent has been introduced shows reduced acid diffusion. However, the resist composition using it is still insufficient to highly control acid diffusion, and its lithography performance is not satisfactory in overall view of resolution, pattern profile, LER, and so on. Moreover, in the electron beam lithography, a superacidic photo acid generator that generates sulfonic acid partially fluorinated as mentioned above is too highly sensitive to improve resolution and LER. This is because the base resin used in the electron beam lithography is mainly composed of protective units with highly reactivity, such as acetal, whereby acid diffusion is apparently increased.